Electromechanical transducer for use as safety and arming device in fuzes



Apnl 1, 1969 R. c. 51. JOHN ELECTROMECHANICAL TRANSDUCER FOR USE AS SAFETY AND ARMING DEVICE IN FUZES Flled March 5 1967 INVENTOR w ROTATIONAL vzlocnv RCHARD C ST'JOHN WUMOQ b Way Maj 874$ United States Patent 3,435,766 ELECTROMECHANICAL TRANSDUCER FOR USE AS SAFETY AND ARMING DEVICE IN FUZES Richard C. St. John, Slrokie, 111., assignor to General Time Corporation, Stamford, Conn, a corporation of Connecticut Filed Mar. 3, 1967, Ser. No. 620,346 Int. Cl. F42c /26 US. Cl. 102-70.2 6 Claims ABSTRACT OF THE DISCLOSURE This application discloses an electromechanical transducer especially suitable for use as a safety and arming device in a fuze. The transducer includes a motor for converting a low power electrical input, as supplied by a battery for example, to continuous rotational movement of a rotor connected to the motor ouput shaft. A pair of spring biased arms are pivoted on the rotor so as to swing out into contact with an arming element at a predetermined speed of the motor, whereby the inertia of the rotor system advances the arming element from a safety position to an arming position.

The present invention relates generally to electromechanical transducers and, more particularly, to an improved electromechanical transducer for use as a safety and arming device in a fuze.

A fuze is generally defined as a device with explosive components for initiating detonation in an article of ammunition by the action of hydrostatic pressure, electrical energy, chemical action, impact, mechanical time, or the like. A safety and arming device is one component of a fuze, and functions to prevent or allow the train of explosives to be detonated.

It is a primary object of this invention to provide an improved electromechanical transducer which is especially suitable for use as a safety and arming device in a fuze application where only a low power source of electrical energy is available. A more particular object of the invention is to provide an electromechanical transducer which is capable of converting a low power electrical input applied to the transducer for some period to a high torque mechanical output.

It is another object of this invention to provide an improved electromechanical transducer of the type described above which can be economically manufactured from only a few parts which can be readily assembled.

It is a further object of this invention to provide an improved electromechanical transducer which can be used for many of the same applications as a rotary solenoid, and yet requires a lower electrical power input than a rotary solenoid.

Other objects and advantages of the invention will become apparent from the following description and upon reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a safety and arming device embodying this invention, with a portion of the arming element broken away to show the internal structure;

FIG. 2 is a vertical section taken along line 22 in FIGURE 1 with the actuating elements in the retracted position;

3,435,766 Patented Apr. 1, 1969 FIG. 3 is a view similar to FIGURE 2 but with the actuating elements in the advanced position for actuating the arming element; and

FIG. 4 is a graph illustrating certain operating characteristics of the device of FIGURES 1 through 3.

Turning now to the drawings, there is shown a portion of a conventional fuze device including a small electric motor 10 having a pair of lead wires 11 for connecting the motor to a low power source of electrical energy, such as a battery, in the fuze device. The motor 10 converts the low power electrical input to a mechanical output by continuously rotating an output shaft 12 along with a cylindrical rotor 13 secured to the shaft. Although the power delivered by the electric motor 10 is normally very small, it will be appreciated that even this low power output is capable of providing relatively high rotational velocities at the output shaft 12 and the rotor 13.

In accordance with the present invention, an arming element is spaced a predetermined distance away from the rotor for arming the fuze in response to movement of the element, and a pair of actuating means are pivoted on the rotor with biasing means urging the actuating means toward a retracted position spaced away from the arming element. The actuating means are adapted to swing outwardly by centrifugal action into engagement with the arming element in response to a predetermined rotational velocity of the rotor so as to actuate the arming element and thereby arm the fuze. Thus, the illustrative device shown in FIGURES 1 through 3 includes an arming element 14 in the form of a metal cylinder which is hollowed out at one end so as to form a sleeve portion 1411 surrounding the rotor 13. The sleeve 14a of the arming element is mounted for rotational movement around the rotor 13, with the angular position of the element 14 determining whether the train of explosives in the fuze is allowed to be detonated. More particularly, the hollow end of the arming element 14 is journaled on a reduced end portion 12a of the motor shaft 12, while the other end of the element 14 is secured to a stub shaft 15 journaled in a frame plate 16.

It is important to note that a continuous clearance is maintained between the inner surface of the sleeve portion 14a and the rotor 13 so that the arming element 14 normally remains stationary while the rotor 13 is rotating. In order to hold the element 14 in a fixed normal position, a spring 17 is secured to the solid end of the cylinder for cooperation with the frame plate 16 to bias the arming element 14 against accidental displacement. Consequently, the arming element is rotated to arm the fuze only when positively actuated by the actuating means associated with the rotor 13.

For the purpose of actuating the arming element 14 at a predetermined rotational velocity of the motor-driven rotor 13, a pair of actuating arms 20, 21 are pivotally mounted on a pair of pins 22, 23 within a pair of complementally formed recesses 24, 25 in the rotor 13. As the rotor 13 is rotated in a counterclockwise direction as viewed in FIGURE 2, the actuating arms 20, 21 tend to swing in a counterclockwise direction about their pivot pins 22, 23 respectively, and advance outwardly toward the arming sleeve 14a due to centrifugal action. This advancing movement is resisted by a pair of biasing springs 26, 27 which urge the actuating arms back toward their retracted positions within the recesses 24, 25.

In keeping with the present invention, the actuating arms 20, 21 and the associated biasing springs 26, 27 are designed so that the actuating arms fly out suddenly against the arming sleeve 14a at a predetermined rotational velocity of the rotor 13. The engaging surfaces of the sleeve 14a and the arms 20, 21 are adapted to provide frictional locking action upon engagement, so that the arming element 14 is advanced against the bias of the resisting spring 17, thereby arming the fuze. Thus, it can be seen that the arming element 13 is effectively actuated in response to a predetermined rotational velocity of the rotor 13.

The opposing forces acting on the actuating arms 20, 21 during rotation of the rotor 13 are illustrated by the curves in FIGURE 4. Thus, the centrifugal force C acting on each arm is represented by curve A, which shows the increasing magnitude of the force C as a function of rotational velocity according to the formula Mw r. The opposing F exerted on each actuating arm by the biasing spring 26 or 27 is represented by the curve B, this spring force remains constant at a given magnitude F until the centrifugal force C has increased sufliciently to deflect the springs outwardly, which is illustrated in FIGURE 4 as occurring at rotational velocity wl. From this point on, the spring force F increases linearly according to the formula F +k1rl', as illustrated by the inclined portion of curve B. As can be seen from the two formulae given above, and as illustrated graphically by curves A and B in FIGURE 4, the centrifugal force C increases exponentially because it is a function of the square of the rotational velocity of the rotor 13, whereas the biasing force F of the deflecting springs increases linearly. Consequently, once the centrifugal force C has reached the level F where deflection of the biasing springs is initiated, the differential between the increasing centrifugal force and the resisting spring bias force escalates rapidly. As a result, the actuating arms 20, 21 fly quickly out into locking engagement with the inner surface of the arming sleeve 14a.

The actuating arms 20, 21 are still rotating along with the rotor 13 as they engage the inner surface of the sleeve 14a, so that the arming element 14 is angularly displaced in the same direction as the rotor 13 (counterclockwise in FIGURE 3), thereby arming the fuze. That is, the arming element 14 is associated with other components of the fuze device so that the fuze is armed in response to the angular displacement of the element 14 effected by the actuating arms 20, 21. It is desirable that the biasing force P of the springs be sufliciently high that the rate of increase in the centrifugal force C is already much greater than the rate of increase of the spring force F at the point where the spring deflection is initiated, e.g., at the arming speed to, in FIGURE 4. Also, the arming speed 0:, must be suflicient to provide the rotor system with suflicient momentum to turn the arming element 14 to the armed position, to carry the rotor system through the arming angle, and to overcome the increased bearing friction.

To render the device self-energizing, i.e., to maintain the actuating arms 20, 21 in locking engagement with the arming element 14 so that they do not retract as the rotor system slows down, the actuating mechanism should be designed so that the combination of the torques due to the frictional force between the arms 20, 21 and the arming element 14 and the centrifugal force of the arms is greater than the torque due to the biasing force of the springs 26, 27 and the friction torque at the pivot points of the actuating arms. These are well known design criteria for self-energizing devices and need not be elaborated upon herein.

It will be appreciated that the electric drive motor is started by a signal from a conventional arming signal device, .and that the time required to bring the motor up to the actuating speed is determined not only by the characteristics of the actuating arms 20, 21, the rotor 13 and the associated biasing springs 26, 27, but also by the start-up characteristics of the motor. It will be apparent that by taking all these factors into consideration, the

response time may be optimized for different fuze applications.

In order to limit the angular movement of the arming element 14, a limit pin 26 is preferably provided on the solid end thereof. The limit in 28 projects into cooperating slot 29 formed in the adjacent frame plate 16 so that as the arming element is rotated by the actuating arms 20, 21, the pin 28 abuts one end of the slot 29 to limit the arming element displacement. Of course, the particular size and shape of the cooperating pin 28 and slot 29 may be varied for different fuze applications.

As can be seen from the foregoing detailed description, the present invention provides an improved electromechanical transducer which is capable of converting a low power electrical input into a high torque mechanical output for a brief interval. While this tranducer is especially suitable for use as a safety and arming device in a fuze application, it is applicable wherever a brief high output energy is required with a limited power input. The electric drive motor is permitted to come up to speed slowly, thereby drawing low input current, while the output energy is stored in the rotating mass of the rotor system. When the rotor system reaches the arming speed at which the actuating arms fly out into engagement with the arming cylinder, the stored energy is dumped rapidly to provide a resultant high output power and torque, relative to the input power and torque. Moreover, the inventive transducer can be economically manufactured from only a few parts which can be readily assembled.

I claim as my invention:

.1. An electromechanical transducer for use as a safety and arming device in a fuze having a low power source of electrical energy, said transducer comprising the combination of an electric motor operatively connected to said power source and including an output shaft, a rotor operatively connected to said output shaft for rotation by said motor, an arming element spaced a predetermined distance away from said rotor and mounted for movement from a safety position to an arming position for arming the fuze, and actuating means pivoted on said rotor and including biasing means urging said actuating means toward a retracted position spaced away from said arming element, said actuating means being adapted to swing into engagement with said arming element by centrifugal action in response to a predetermined rotational velocity of said rotor so as to actuate said arming element.

2. An electromechanical transducer as defined in claim 1 in which said arming element comprises a sleeve surrounding said rotor, and said actuating means comprise a pair of arms pivoted on said rotor and adapted to swing out beyond the periphery of said rotor into locking engagement with the inner surface of said sleeve so as to rotate said sleeve through a predetermined angular displacement.

3. An electromechanical transducer as defined in claim 1 which includes biasing means associated with said arming element for holding said element in the safety position until said element is engaged by said actuating means.

4. An electromechanical transducer as defined in claim 1 which includes limiting means associated with said arming element for stopping the movement of said element at said arming position when said element is actuated by said actuating means.

5. An electromechanical transducer as defined in claim 1 in which said rotor is fixed to said output shaft of said motor and said arming element is journaled on said shaft for rotational movement along with said rotor when engaged by said actuating means.

6. An electromechanical transducer for use as a safety .and arming device in a fuze having a low power source of electrical energy, said transducer comprising the combination of an electric motor operatively connected to said power source and including an output shaft, a rotor fixed to said output shaft for rotation by said motor, said rotor including actuating means spring biased toward a retracted position and adapted to swing to an advanced position by centrifugal action at a predetermined rotional velocitytof said rotor, and an arming element positioned for engagement by said actuating means at said advanced position whereby the momentum of said rotor and actuating means advances said arming element from a safety position to an arming position.

6 References Cited UNITED STATES PATENTS VERLIN R. PENDEGRASS, Primary Examiner. 

